1. Field of the Invention
The present invention relates to a dielectric ceramic composition sinterable at a low temperature, a complex electronic device and multilayer ceramic capacitor having the dielectric ceramic composition as a dielectric layer.
2. Description of the Related Art
With a demand for reduction in size and weight on an electronic hardware equipped with an electronic device, a demand for small multilayer electronic device is rapidly increased. Also, as a plurality of the electronic devices is placed on a circuit substrate, a multilayer filter as a type of complex electronic devices, wherein a coil and a capacitor is integrated, has been used against a high-frequency noise of the circuit substrate.
Since such a multilayer filter is an electronic device having a coil portion as well as a capacitor portion, in the production process, it is necessary to co-fire a magnetic material constituting the coil portion and a dielectric ceramic composition constituting the capacitor portion. In general, ferrite used as the magnetic material constituting the coil portion is low in sintering temperature, which is 800 to 900° C. Therefore, a material of the dielectric ceramic composition used in the capacitor portion of the multilayer filter is required to be sinterable at a low temperature.
For example, Japanese Patent No. 3030557 proposes a dielectric ceramic composition for low-temperature firing, which can be co-fired with an Ag-based internal electrode by adding a specific amount of glass to a main component comprising SrTiO3 added with CuO, or MnO if needed.
On the other hand, with a recent trend to further downsize an electronic hardware, a demand for reduction in size and height of a multilayer filter are growing. To reduce the size and height of the multilayer filter while maintaining its performance, it is particularly necessary to reduce the size and thickness of a dielectric layer in a capacitor portion.
However, in Japanese Patent No. 3030557, the thickness of a dielectric layer comprised of a dielectric ceramic composition is 50 μm, and therefore, when making the layer thin, the reliability is not be secured. Also, since the dielectric ceramic composition disclosed in Japanese Patent No. 3030557 includes a relatively high content of a glass component, a grain size may be too large or a crystalline texture may be uneven, so that it is considered difficult to make a layer thin. Further, when the content of the glass component becomes too large, there is a problem that a plating solution goes into an inside of a body (a multilayer portion) when forming an external electrode as well as a tendency to reduce a specific permittivity. Also, too large amount of CuO results in segregation, causing a problem to reduce insulation resistance.